These developments come after a series of rebel victories in recent days and suggest that President Bashar Assad's government is facing increased pressure from the rebels in an uprising now 20 months old.

It wasn't clear why the Internet went down. The Syrian government insisted service was only cut in some areas and gave conflicting accounts, saying that it was a technical problem and that it was caused by a rebel attack, The Associated Press reported.

Two U.S. companies that monitor Internet traffic, Renesys and Akamai Technologies, said that Syria was effectively dropped off the Internet shortly after noon Thursday, Syrian time.

The Syrian government has severed phone lines and Internet service in some areas when carrying out military operations, but there has not previously been such a comprehensive blackout.

And outside Damascus, the road to the airport was closed due to fighting between rebels and government troops, according to the Syrian Observatory for Human Rights, a group that backs the opposition in Syria.

Rebels have been active outside Damascus in recent days and there has been increasing talk about a major rebel assault on the city.

Update at 5:40 p.m. ET: 'A Blanket Disconnection'

Jim Cowie, the chief technology officer at Renesys, told All Things Considered that "the domestic Internet of Syria disappeared from sight over the course of three to four minutes. Very quickly. It really does look like a switch being thrown if you look at the data."

This was unlike anything that's happened previously in Syria, he added.

"The government has turned off the Internet in specific cities, for specific operations [in the past]," he said. "What we're seeing today is a blanket disconnnection of the national insfrasturcre from the global infrastructure."

Also today, The Associated Press writes that "the Obama administration is preparing to recognize Syria's new opposition council as the legitimate representative of the Syrian people in the coming weeks, paving the way for greater U.S. support for groups seeking to oust President Bashar Assad's regime, officials said Thursday. Announcement of the move — which has already been taken by several U.S. allies — is planned on or around a conference of more than 70 nations in Marrakesh, Morocco, on Dec. 12. Secretary of State Hillary Rodham Clinton is planning to attend the latest so-called Friends of Syria gathering."